A plasma display panel (hereinafter referred to simply as a PDP) allows achieving a high definition display and a large-size screen, so that television receivers (TV) with large screens of as large as 100 inches diagonal length can be commercialized by using the PDP. In recent years, use of the PDPs in high-definition TVs, which need more than doubled scanning lines than conventional NTSC method, has progressed. The PDP has been demanded to further reduce the power consumption in order to meet the energy-saving trend, and the PDP free from lead (Pb) has been also required in order to contribute to environment protection.
The PDP is basically formed of a front panel and a rear panel. The front panel comprises the following structural elements:                a glass substrate made of sodium-borosilicate-based float glass;        display electrodes, formed of striped transparent electrodes and bus electrodes, formed on a principal surface of the glass substrate,        a dielectric layer covering the display electrodes and working as a capacitor; and        a protective layer made of magnesium oxide (MgO) and formed on the dielectric layer.        
The rear panel comprises the following structural elements:                a glass substrate;        striped address electrodes formed on a principal surface of the glass substrate,        a primary dielectric layer covering the address electrodes;        barrier ribs formed on the primary dielectric layer; and        phosphor layers formed between each one of the barrier ribs for emitting lights in red, green, and blue respectively.        
The front panel confronts the rear panel such that its electrode-mounted surface confronts an electrode-mounted surface of the rear panel, and peripheries of both the panels are sealed in an airtight manner to form a discharge space between these two panels, and the discharge space is partitioned by the barrier ribs. The discharge space is filled with discharge gas of Neon (Ne) and Xenon (Xe) at a pressure ranging from 400 Torr (53300 Pa) to 600 Torr (80000 Pa). The PDP allows displaying a color video this way: Voltages of video signals are selectively applied to the display electrodes for discharging, thereby producing ultra-violet rays, which excite the phosphor layers for each color, so that colors in red, green, and blue are emitted, whereby a color video can be displayed.
The PDP discussed above is driven, in general, by a driving method which has an initializing period for adjusting wall charges into an easy-addressable state, an address period for carrying out address-discharge in response to input video signals, and a sustain period for displaying a video by generating sustain-discharge in a discharge space where an address has been done. A time span formed of the foregoing periods combined together is referred to as a subfield, and this subfield is repeated several times within one field corresponding to one frame of a video, thereby achieving a gray scale of the PDP.
The protective layer formed on the dielectric layer of the front panel of the foregoing PDP is expected to carry out the two major functions: (1) protecting the dielectric layer from ion impact caused by the discharge, and (2) emitting primary electrons for generating address discharges. The protection of the dielectric layer from the ion impact plays an important role for preventing a discharge voltage from rising, and the emission of primary electrons for generating the address discharges also plays an important role for eliminating an erroneous address discharge because the error causes flickers on videos.
To reduce the flickers on videos, the number of primary electrons emitted from the protective layer should be increased. For this purpose, impurities are added to magnesium oxide (MgO), or particles of MgO are formed on the protective layer made of MgO. These instances are disclosed in, e.g. Patent Literatures 1, 2, 3, 4 and 5.
In recent years, a higher definition has been required to TV receivers. The market thus requires the PDP to be manufactured at a lower cost, to consume a lower power, and to be a full HD (high-definition, 1920×1080 pixels, and progressive display) with a higher brightness. The characteristics of emitting electrons from the protective layer determine the picture quality, so that it is vital for controlling the electron emission characteristics.
To be more specific, a video of higher definition needs a greater number of pixels to be addressed although a time for one field is kept as it has been, so that a width of a pulse, within an address period of a subfield, for applying a voltage to address electrodes should be narrowed. However, a time lag is present between a rise of a voltage pulse and a discharge into the discharge space. This time lag is referred to as a discharge delay. A narrower pulse width thus lowers a probability of ending a discharge within an address period. As a result, a defective lighting occurs and flickers which degrade a video quality are produced.
A partial pressure of xenon (Xe) can be increased for improving an efficiency of light emission produced by the discharge so that the power consumption can be lowered. However, a greater discharge voltage invites a greater discharge delay, thereby incurring a defective lighting which degrades a video quality.
As discussed above, the progress of PDP of higher definition and lower power consumption should be accompanied with the following two measures simultaneously: (1) avoid increasing a discharge voltage, and (2) decrease defective lightings to improve a video quality.
A protective layer added with impurities has been tested whether or not this addition can improve the electron-emission characteristics; however, in a case where the characteristics can be improved, electric charges are stored on the surface of the protective layer to be used as a memory function. The number of electric charges decreases greatly with time, i.e. an attenuation rate becomes greater. To overcome this attenuation, measures is needed such as increment in an applied voltage.
On the other hand, forming the crystal particles of MgO on the protective layer made of MgO allows reducing a discharge delay, thereby lowering the number of defective lightings; however, the discharge voltage cannot be lowered.
The present invention addresses the foregoing problems, and aims to provide a PDP which can display a video of a higher brightness and yet can be driven at a lower voltage.    Patent Literature 1: Unexamined Japanese Patent Application Publication No. 2002-260535    Patent Literature 2: Unexamined Japanese Patent Application Publication No. H11-339665    Patent Literature 3: Unexamined Japanese Patent Application Publication No. 2006-59779    Patent Literature 4: Unexamined Japanese Patent Application Publication No. 08-236028    Patent Literature 5: Unexamined Japanese Patent Application Publication No. H10-334809